The present invention relates generally to diagnosing, or troubleshooting, problems or failures in vacuum systems. More specifically, the present invention relates to a method for quickly determining the location or cause of a failure in the ability of a vacuum system to create or maintain a desired vacuum setpoint pressure for the manufacturing of silicon wafers.
A silicon wafer is the material on which integrated circuit (IC) chips are made. The manufacturing of IC chips requires a very high-vacuum environment. A suitable high-vacuum environment may be created with a properly designed and manufactured vacuum system. Vacuum systems for the manufacturing of IC chips on silicon wafers are generally known. There are many associated parts to a vacuum system, but it can generally be described as having two main sections: the pump and the chamber. These two sections are generally divided by a gate valve, which seals the two sections off from each other.
After assembling a vacuum system, the vacuum system is tested at a high vacuum setpoint pressure at least as high as the vacuum that it will be expected to achieve when actually manufacturing IC chips on silicon wafers. The vacuum test essentially qualifies the system to be operated at pressures up to the high vacuum setpoint pressure. This test may take up to several hours or days to perform, because the first time that a new system is subjected to a high vacuum, various types of impurities and contaminants may be in the system, having been introduced into the parts of the assembly during its manufacture. The impurities and contaminants will desorb from the surfaces of the interior of the system when subjected to a vacuum. A greater contamination will cause a faster desorption rate of gases from the interior surfaces into the interior space, and a faster introduction of gases into the interior space results in a longer time to achieve the setpoint pressure. A vacuum system may become recontaminated after the first vacuum period, but typically not to the extent of contamination prior to the first vacuum period, so the vacuum test typically takes longer to achieve the setpoint pressure than do subsequent vacuum periods. The bakeout period is the time that the system is subjected to a high vacuum, during which the impurities and contaminants are desorbed and removed from the interior of the system, prior to determining the setpoint pressure. The vacuum test ends when the vacuum of the system reaches the desired vacuum setpoint pressure and is able to maintain it after the expected time for the test has elapsed.
If the vacuum system fails the test, then it will have to be fixed, or the system will have to be scrapped. These vacuum systems can be very expensive, making it very undesirable to have to scrap an entire system. Therefore, the manufacturer of the system will usually try to troubleshoot the problem in order to save the system. Troubleshooting involves diagnosing the problem and repairing it.
The base pressure of a vacuum system is the lowest pressure down to which the system can be pumped. If the base pressure can reach or exceed the qualifying base pressure, the setpoint pressure, e.g. 6.0xc3x9710xe2x88x929 torr, then the vacuum system has passed the vacuum test. The base pressure is determined by measuring the pressure after bakeout while the pump holds the system steady at the ultra high vacuum. If the base pressure has not reached the qualifying base pressure, then the vacuum system has failed the base pressure test, and troubleshooting may be required.
The rate of rise (ROR) of a vacuum system is the rate at which the pressure inside the chamber rises after the chamber has been isolated from the pump by closing the gate valve. The ROR is measured by closing off the gate valve and measuring the pressure over a period of time, e.g. 2 minutes. If the pressure rises slowly enough, e.g. at a qualifying ROR of 1.5xc3x9710xe2x88x926 torr/2 min or less, then the vacuum system has passed the ROR vacuum test. If the pressure rises faster than the qualifying ROR, then the vacuum system has failed, and additional troubleshooting may be required.
Troubleshooting involves determining the cause of the base pressure and/or ROR failure. Problems arise when the nature of the cause is not readily apparent. An operator may replace various components of the vacuum system and then retest the system, but without a clear indication of the nature of the cause of the failure, the operator is left uncertain over which parts to replace. Indiscriminate or random replacement of components and retesting can be both timeconsuming and costly.
It is, therefore, desirable to have a method of diagnosing a vacuum system that has a failed base pressure or ROR, that quickly identifies the most likely cause of the failure.
Generally, a method for locating the cause of a failure in a vacuum system includes determining whether the base pressure (Pb), or rate of rise (ROR), or both has failed. This failure information is then compared with known categories of failure for various components or sections of the vacuum system, including the chamber or the pump.
One category of failure may be: the Pb has failed and the ROR has not failed. This category suggests that the pump is most likely responsible for the failure. Another category of failure may be: the base pressure has not failed and the rate of rise has failed. This category suggests that the chamber is most likely responsible for the failure. A third category of failure may be: the base pressure has failed and the rate of rise has failed. This category suggests that the chamber is most likely responsible for the failure.
Measurements with an RGA of the partial pressures of certain residual gases in the system may indicate a leak in the system when relative partial pressures of some of the residual gases are higher than certain others. Additionally, a bakeout lamp, containing a gas, may be used in the chamber to heat the chamber during vacuum testing, and a leak from the lamp may be indicated when the partial pressure of the same gas that is in the lamp changes as the lamp is turned on and off.
The cause of a failure in either section may be further narrowed by comparing the quantities of certain substances in the system, measured by an RGA, wherein a leak may be indicated when one or more particular substances is present in a greater quantity than expected. Additionally, the location of a leak may be determined by moving a source of a particular gas around the outside surface of either section while monitoring the quantity of that substance in the system, so that when the quantity of the substance in the system goes up, the location of the leak is determined.